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SOIL & WATER MANAGEMENT & CONSERVATION

Extension of an Existing Model for Soil Water Evaporation and Redistribution under High Water Content Conditions

^a Agricultural and Biological Engineering Dep., Univ. of Florida, P.O. Box 110570, Gainesville, FL 32611
^b Dep. of Land, Water and Environment, Univ. of Jordan, Amman, Jordan

^* Corresponding author (cporter{at}ufl.edu).

Most crop, hydrology, and water quality models require the simulation of evaporation from the soil surface. A model developed by J.T. Ritchie in 1972 provides useful algorithms for estimating soil evaporation, but it does not calculate the soil water redistribution resulting from evaporation. A physically-based model using diffusion theory, described previously by Suleiman and Ritchie in 2003, provides efficient algorithms for soil water redistribution and soil evaporation. However, the model is appropriate only for second stage drying when the soil in the entire profile being simulated is below the drained upper limit (_DUL) and no more drainage occurs due to gravity. This paper extends the Suleiman–Ritchie model for soil water contents higher than _DUL where soil evaporation rates are usually higher than second stage drying. New algorithms were developed for these wetter conditions that are functions of soil depth and the wetness of the near-surface soil. New model parameters were calibrated with data measured in laboratory soil column studies. The resulting model was integrated into DSSAT-CSM (Decision Support System for Agrotechnology Transfer Cropping Systems Model). Simulated soil evaporation rates and soil water contents obtained using the Suleiman–Ritchie model with the developed extensions and the previous DSSAT soil evaporation model were compared and evaluated with field measurements of soil water content during several drying cycles for parts of 3 yr in North Central Florida. Computed soil water contents from the model agreed well with the measured soil water contents near the surface, and provided more accurate estimations than the original DSSAT soil evaporation model, especially for the 5-cm surface layer.

Abbreviations: _DUL, Soil water content at drained upper limit (cm³ cm^–3) • CSM, Cropping Systems Model • DSSAT, Decision Support System for Agrotechnology Transfer • ES, evaporation of water from soil surfaces (cm) • ESR, Extended Suleiman and Ritchie soil evaporation model • LAI, Leaf area index (m² m^–2) • MAE, mean average error • MicroWEX, Microwave, Water, and Energy Balance Experiment • ORD, Original Ritchie DSSAT soil evaporation model • SR, Suleiman and Ritchie method of soil evaporation using diffusion theory